The present invention relates to a measuring device and measuring method and, more particularly, to a measuring device and method for measuring a torque in rectangular or square preformed orthodontic arch wires.
Arch wires of the aforementioned type disclosed in, for example, U.S. Pat. No. 4,424,033 are used in conjunction with tooth brackets for correction of all classes of malocclusions using edgewise or like wire techniques. In corrections using arch wires, the brackets are secured to the teeth of the patient by the use of bands to which the brackets are welded or by cementing brackets directly to the teeth. Generally, in each number of stages during the course of the treatment, an arch wire is secured to the brackets. As the treatment progresses, the arch wire which is used more or less closely approaches the ideal arch form thereby progressively correcting misalignments of the teeth of the patient.
Arch wires for orthodontic appliances may be formed from straight wire blanks by techniques such as disclosed in, for example, U.S. Pat. No. 4,566,305 wherein the wire blanks are formed into arches by way of a swing-arm bender.
One problem with arch wires resides in the fact that when the wires are formed, the wires may have a certain internal torque therein resulting from, for example, the forming of the arch wire. The existence of such torque creates difficulties when the arch wires are used with so-called pre-torqued wire brackets which generally have a slot for accommodating the arch wires, with the brackets having a preset predetermined torque.
If an arch wire has no internal torque no difficulties are created since the orthodontist will know the preset degree of torque in the bracket and can reasonably assume that a certain amount of torque will be placed on the tooth being corrected. However, if due to, for example, forming of the arched wires, shipping, or subsequent handling or the like, the arch wire develops an internal torque, and such torque will either increase or decrease the amount of torque set by the pre-torque tooth bracket depending upon which way the arch wire is inserted into the bracket.
Conventionally, orthodontist have used a very simple test to determine whether an arch wire has a torque. More particularly, the arch wire is simply placed on a flat plate glass, pressed at the center of the arch, and then turned over and the same operation is carried out. If a torque exists in the arch wire, the legs of the arch will move upward in one of the two positions being tested, since, in the other of the two positions, the legs will be forced down by the torque in the arch wire into the glass.
While the above conventional technique does easily ascertain whether a torque exists, such technique does not provide any accurate measurement of just how much torque exists in the arch wire.
Another technique has been proposed utilizing two pair of orthodontic pliers, with one pair of the pliers being placed adjacent to a leg of the arch wire while the other pair of pliers is placed at the other leg. The orthodontic pliers open and close alternately and at a 180.degree. out of phase with one another. Consequently, as one of the pair of pliers is closing on one leg of the wire, the other pair of pliers will be opening. If a torque exist in the wire, the leg adjacent to the pair of pliers which is opening will move the opened jaws.
While this last proposed technique also provides a simple test for determining the existence of the torque, it does not provide any degree of measurement for just how much torque exist in the arch wire.